Catalytic conversion of hydrocarbons



Patented F eb. 29, 1944 CATALYTIC CONVERSION OF HYDROCARBONS Charles L.Thomas, Chicago, Ill., assigner to Universal Oil Products Company,Chlcagollll., a corporation of Delaware Application January 8,1940,serial No. 312,861.

` vUNlj'lED STATES. PATENT; OFFICE 12 claims. (c1. 19o- 49) Thisinventionrelates to the conversion of hydrocarbon oil'to produce largeyields of high antiknock gasoline `for automotive and aviation purposes.The hydrocarbon oil fractions proc-` essed may be from petroleum or fromhydrocarbonaceous sources generally, including synthetically'producedhydrocarbon mixtures or primary distillates produced in the destructivedistillation of hydrocarbon-containing materials such as coals, lignitesand shales. l The hydrocarbon fractions directed to contact with thecatalysts are more usually of a distillate character and are vaporizableAvlfithout substantial decomposi- More specifically the' invention isconcerned with the production of automotive and aviation fuels'concurrently from the hydrocarbon oils in thermal-catalytic `operationswhereby maximum utilization ofthe hydrocarbons' is made in thueproduction of the two fuels. In the'flrst step of the process,automobile blending fuels are made having high antiknock value. Theirhigh antiknock value is vapparently Vdue to the highly branchedstructure of the hydrocarbons present,

' especially the oleflnswhich constitute the large or'rnajor proportionof the' product. In the second stepvof the 'process the low'boilingrange product has not only a high antiknock value but also a highcontent of saturated hydrocarbons. Consequently it has improvedproperties with respect to storage stability, susceptibility to addedantidetonating agents, and blending value, and

requires little or no additional rening treatment. The preferredcatalystsy are characterized by their selectivity inacceleratinggasoline-forming rather than gas-forming reactions, by theirrefractory character which enables them to retain theircatalytic,propertiesr over long periods of time under commercialconditions ofv use and regeneration, and by their ease and simplicity ofmanufacture and their exact reproducibility..

The art of pyrolytically cracking relatively heavy hydrocarbons toproduce primarily motor fuel 'and/or gas is very extensive and it isrecognized that most of thebaslc principles of hydrocarbon decompositionby thermal treatment are known and particular commercial processes havebeen developed which embody these principles. Where it is desirable toproduce motor'fuel having octane numbers much above 70, pryolyticcracking and reforming processes carried out undersubstantial pressureappear to be limited by the fact that higher antiknock properties areobtained only with decreased yields of gasoline,-

apparently dueto some recracking of the gasoline taking place. Whencatalysts are introduced, however, to modify the conversion reactions,very little is generally known about the specific nature of thehydrocarbon reactions involved and the manner of the catalyst operation,

especially where the'catalyst has 'to serve as in commercial practice,for-'long periods of time' under the relatively high temperatureconditions of repeated use and regeneration. Due tothe complexity of thehydrocarbon conversion reactions and the highly adsorptive character ofcatalytically active surfaces, even a highly eective catalyst can onlybe used for a relatively small fraction of its total period ofusefulness before it must be regenerated luy-oxidizing treatment' toremove l(Azarbonaceous materials. `T01 meet 4commercial vrequirements asa cracking catalyst, for example, it must withstand a large number ofthese regenerations without a large loss in the initial activity. Manysubstances are vdescribed i'n technical publications and in the patentliterature which have catalytic properties in modifying thermalhydrocarbon conversion reactions, but investigation has shown that thesesubstances, practically without exception, while having some measure ofthe activity required of a commercial catalyst on the initial contactwith the hydrocarbons, have little or no activity when carbonaceousmaterials which normallydeposit upon the catalyst in the hydrocarbonconversion reactions are removed by oxidation. The active surfaces arepartly or wholly destroyed during the initial contacts or in the initialregeneration treatmenm so that theprepared substances have academicinterest but no commercial value.` Even where catalysts havev beenreported to have commercial possibilities, extreme care has beenemployed in their use andregeneration in order to retain the initialactivity and structural formof the catalyst. The

of high antiknock gasoline, separating the conversion products toproduce a normally gaseous fraction, said high antiknock gasoline, anintermediate higher boiling fraction, and a. high boiling residuefraction to be withdrawn from the process, recovering the high antiknockgasoline containing large proportions of oleflnic hydrocarbons as aproduct of the process, and directing said intermediate higher boiiingfraction from the primary step to further catalytic treatment in asecondary step where the hydrocarbon fraction is vaporized and contactedwith a. similar catalyst as in the first step at a teme perature withinthe approximate rangeV of 500- 850 F. and at a pressure of approximately50 to 1000 pounds per square inch to produce conversion productscontaining large proportions of a relatively saturated gasoline,separating the conversion products to produce a normally Vgaseousfraction, said relatively saturated gasoline, and a higher boilinghydrocarbon fraction, recovering the relatively saturated gasolinefraction as a product of the process suitable for use in the manufactureof aviation 4fuels and returning saici higher `oloiling fraction fromthe secondary step to further Contact with the catalyst in the primarycracking step.

oil charged hourly per volume of catalyst spacel in the reactor. Spacevelocities more generally employed in this step range from approximately2 to 10. The preferredtemperatures more usuf ally range from 900-1000F.depending in general upon vthe particular charging stoclrand the depthof cracking. The gasoline fraction produced usually contains oleflnichydrocarbons of the order of 40-70% or more and has an octane number ofapproximately 78-80 by the motor method. It cannot be readily treatedand converted to a substantially saturated gasoline of the highantiknock value required of aviation fuels. It has, however, anantiknock value higher than that used in fuels for automobile theoperating conditions employed in the secondengines at the present timeso that it is highly desirable for blending with gasoline fractions ofinferior antiknock value toproduce automobile fuels of the currentmarket grade. Y,

The normally gaseous fraction separated from the conversion products,especially in the primary step contains a relatively large proportion ofolenic hydrocarbons, particularly C3 and C4.

olens which .may be advantageously utilized using known polymerizationor alkylation processes to obtain further yields of high antiknockgasolines. In these processes, prepared catalysts such as aluminumchloride, phosphoric acid, sulfuric acid, boron fluoride mixed withhydrogen fluoride, etc.,`may be used. Saturated gasoline hydrocarbonsare produced directly by alkylation treatment while with polymerizationtreatment saturated gasoline may be obtained bythe use of additionalprocessing involving hydrogenation. v In the secondary step of thepresent invention higher boiling hydrocarbons separated from theconversion products of the primary step are more usually processed undernon-hydrogenating cracking conditions. Temperatures bf HOO-800 F. andthe liquid space velocities employed may range from approximately 0.5 to5, the lower space velocities within this range being more generallyemployed. Although atmospheric and slightly shperatmospherio pressurehave been ary step, the degree of saturation of the gasoline product ispartly dependent upon the .charging stock admitted to the process andthe depth of cracking carried out in the primary step. Charging stocks,for example, which are relatively deiicient in hydrogen with respect totheir aliphatic or cyclic character, or stocks which vhave been toodeeply cracked in the primary step will produce less saturated productsin the secondary step. More usually the process of the present inventionis carried out so that the two steps are in balance and a maximum overall yield of gasoline is produced in the two steps. It appears that thehigher boiling hydrocarbons separated from the gasoline product in theprimary step are particularlyy amenable to catalytic treat" ment for theformation of relatively saturated gasoline hydrocarbons. Although theolenn content of the gasoline produced in the secondary step is usuallysumciently low for vdirect use in preparing aviation fuel. the gasolinefraction may be subjected to additional chemical treat ment to reducethe olefin content by conventional processes. In any event therelatively saturated gasoline resulting in the secondary step of thisprocess has high storage and color stability, a low copper dish gumcontent and a relatively low sulfur content since considerable` sulfuris eliminated largely as hydrogenv sulde from sulfurcontaining oilduring the catalytic conversion reactions. Because of thesecharacteristics, the high antiknock value and the high susceptibility tofurther increase in antiknockvalue by the addition of tetraethyl lead.this gasoline is especially desirable as an aviation base fuel.

A fraction such as the 3D0-400 F. cut may be separated from theconversion products of the secondary step and because of its highantiknock value be used for blending purposes in preparing automobilefuels. Higher boiling fractions are preferably returned to the primarystep for further catalytic cracking treatment in the production ofautomobile fuels. In some cases, however, this oil has been relativelyhighly degraded and may be withdrawn from the proc-r ess as such ordirected tov separate cracking treatment for its maximum utilization inmotor fuel production under optimum conditions.

The catalyst used both in the primary and secondary steps is preferablyof the synthetic type. Although naturally occurring materials such asacid-treated clays including fullers earth, montmorillonite type clays,some bentonites, etc., may be utilized with or Without added activatingmetal compounds the results are not equivalent to those obtained whenusing the preferred aesaoss with a precipitated hydrous metal oxide suchas alumina, zirconia, or mixtures thereof present in minor proportions.According to one general method of preparation the hydrated'silica may'4be precipitated from a' solution of commercial water glass andsubsequently admixed with the remaining hydrous oxide components. Thewater glass maybe diluted to the-extent of 8 to 10 times and an acidsuch as hydrochloric acid added to precipitate the hydrated silica. Theconcentration and excess acid utilized Yare regu,- lated so as to obtainoptimum precipitating conditions and the hydrated silica. may then beltered to remove the mother liquor. The hydrated silica may then beadmixed with the hydrous oxide components in any suitable manner as forexample by suspending the precipitated hydrated silica in a solution ofsalts of the metal components for which the hydrous oxides are desired,

ence of the suspended hydrated silica by the addition oi an alkalineprecipitant, more usually ammonium hydroxide. According to this promeshwhich may applyto either shaped particles terial in tubes or chambers inthe form of small pellets or granules. may vary within the approximaterange of- 2-10 of uniform size such as short, essentially cylindricalshapes, for example, or particles of irregular4 shape produced byconsolidating and sizing the powdered catalytic material. method ofpreheating the hydrocarbon oil to be processed in each stage to atemperature suitable for conversion in `contact with the catalyst,'andthen passing the vapors over a stationary mass of thecatalystparticlesjrnay be employed. The

, preheated vapors may be passedY through the cedure the precipitatedhydrated silica may be slurred in a solution o zirconyl chloride and/oraluminum chloride for example in amounts adequate to produce hydrousoxides in the desired proportions, and ammonium hydroxide added toprecipitate said hydrous oxides. Various other procedures may befollowed, however, wherein these components may be co-precipitated orseparately precipitated to intimately adrnix the components. Thehydrated silica may beheated in solutions of the metal salts and hydrousoxsilica by hydrolysis, or the precipitated hydrated silica may beadmixed with a relatively con-A' centrated solution of themetal salt toiorm a paste Aand then heated to deposit the desired metal oxides. Theadmixed materials are usually dried at ordinary drying temperatures andreduced to a powdered condition for formingim to shaped and sizedparticles. According to other procedures it is possible to extrude .thecatalytic material While in a wet condition and subsequently dry themoist particles to obtain them in the desired form. y

In the manufacture of refractory -synthetic catalysts it has been foundnecessary Where sodium compounds have been adsorbed intothe cat alyticmaterial during preparation to treat the material at some stage of itspreparation in order to remove these alkali metal impurities. This maybe accomplished according to one procedure by washing ther driedcomposite with acidulated water until the alkali metal impurities havevbeen substantially eliminated.. The material is then again dried andformed into particles usually with a lubricant added .to facilitatecohesion and prevent adhering or sticking in the briquetting or pillingmachines used in forming the material into pills, pellets or otherconsolidated and shaped particles. Subsequently the formed particles areheated at temperatures of the order of lOOO-lOlPF. whereby the catalystassumes a suitable form' for prolonged use in the treatment v ofhydrocarbons. The catalysts are highly porous and possess a large totalcontact surface. They are not dlfiicult to reactivate by oxidation andretain their high degree of activity during high temperature conditionsof alternate use and reactivation for long periods of time.

In both steps rof the present invention the cata.- lysts may beconveniently utilized as filling macatalyst in apparatus where thepassageof vapors is restricted to denite paths rather than allowing thevapors to have unrestricted contact with large bedsof catalyticmaterial.' This facilitates vcontrol of the temperature of the contact`materi`als both in processing and during regeneration by using variousheat interchange clevices and media. Since the commercially usefulactive periodof the preferred catalystsisof relatively shortdurationbeore carbonaceous materials deposited thereonhave to 'beremoved by oxidation, a plurality of reaction vessels are used in eachstep so that a continuous operation may be had byregenerating partiallyspent catalyst.

out of contact withthe stream of hydrocarbon 'vapors While processinghydrocarbons in contact with the active catalyst. Conversion productsremoved from both steps of the process are separately fractionated andSeparated to produce a normally gaseous fraction, the gasoline boilingrange fraction and higher. boiling hydrocarbons, the major portion ofthe higher boiling hydrocarbons removed from the primary step beingprocessed in the .secondary step and the higher boiling hydrocarbonsfrom the secondary Step preferably returned to further crackingtreatment in the primary step.

Generally speaking, a suitable aviation base fuelniay be produced inthesecondary step by varying the conditions of temperature, pressure,

.-' space velocity and lengthof period, these conditions varying moreork less with the boiling range and type of hydrocarbons undergoingtreatment. More usually additional treatment of the' product is notnecessary but the process may be operated in such a manner thatArelatively minor propor-v tions of unsaturated hydrocarbons remaining in'illustrating l, the process provided by the inven- Referring to thedrawing, the initial charging oil for the processzis suppliedthroughline l to the high temperature catalytic cracking zone 2 wheren it iscatalytically converted in the manner previously described to producegasoline of relativelyhigh olefin content and higher boiling lquidfractions amenable toiurther treatment for the production of gasolinelow in or substantially devoid of oleilns.

There will normally be an vincidental produc-r n tion of gas and someheavier liquid conversion products in zone 2 and the resulting fluidprode.

ucts are supplied through line 3 to separation in zone Wherefrorn gaseslighter than yor in excess of those desired for inclusion in the01efinic gasoline are discharged through line 5- and whererom any heavyliquid products, unsuitable The average particle size The simplev forthe subsequent further treatment provided, are withdrawn through line 6.Gasoline of the desired vapor pressure and boiling range and having arelatively high olefin content is separately removed from separatingzone 4 through line 1.

Intermediate liquid conversion products boiling above the range of thegasoline removed through line I are directed from separating zone 4through line 8 to the low temperature catalytic cracking zone 9. 1

In zone 9 the oil supplied thereto from the initial cracking step issubjected to treatment in the manner previously specified to producegasoline fractions substantially devoid of olefins or of materiallylower olefin content than the gasoline recovered from the initialconversion step. The resulting fluid conversion products are directedfrom zone 9 through line I0 to 4separation in zone II wherefrom normallygaseous fractions undesired for inclusion in the gasoline product ofthis step are discharged through line I2. 'Any heavy residual liquidproducts may be removed from separating zone II through line I3. Thegasoline product of the desired vapor pressure and boiling range, whichis relatively low and/or substantially devoid of olens, is directed fromseparating zone II through line I4 to storage or elsewhere as desired.In the preferred embodiment of the'invention this product willconstitute an aviation base stock of good antiknock value and lowbromine number suitable for blending with the other usual ingredients ofaviation gasoline to form a product meeting specifications for aviationfuel.

Intermediate liquid conversion products boiling above the range of theproduct withdrawn through line I4 are removed from the separating zonethrough line I5 and may be discharged from the system to storage vorelsewhere as desired or they may be returned all or in part through lineI5 to further catalytic cracking treatment in zone 2 together with theinitial charging oil.

The following speciiic examples are given to illustrate the process ofthe invention and the type of catalyst preparation preferably utilized.The process should not ber considered as limited to these examples ofthe process or to the particular catalyst preparation, these being givenas illustrative of the novelty and utility of the invention.

Example I In this example the cracking catalyst used in both the primaryand secondary steps was a calcined alkali metal-free composite ofprecipitated silica, alumina and zirconia in the following molal ratio:100Si02z2Al2O3r5ZrO2. A commercial water-glass grade of sodium silicatecontain-` ing approximately 28.5 per cent of silicon dioxide and 9 percent by vweight of sodium oxide was diluted with approximately i0volumes of water. Hydrochloric acid was added gradually and withconstant agitation of the mixture until it was barelyalkaline tophenolphthalein. After the silica gel has formed and has been wellbroken up, a small additional amount of hydrochloric acid vwas addeduntil the mixture was just y acid to Congo red, whereby substantiallycomplete precipitation w'as effected. The silica gel sus pension wasthen brought back practically to'a neutral point when tested with litmusand charged to a lter. The cake on the filter was then removed, brokenup and thoroughly agitated and slurried in a solution containingaluminum and zirconyl chlorides in amounts sufficient to give thedesired final composition above noted. Ammonium hydroxide was' thenadded to the slurry until the mixture was just barely acid to litmusafter which the material was again nltered. The lter cake was removedand dried to a water content of approximately per cent after which itwas ground to pass a 30 mesh screen. The powdered material was washedwith acidulated water until the washings gave no further test for sodiumusing magnesium uranyi acetate reagent. The purled material was thendried, admixed with a lubricant and pilled to form 1/8 inch cylindricalparticles. The pilled particles were calcined at 1500 F. for about onehour to produce the catalytic material in its final active form andstabilize it with respect to subsequent exposure to the hightemperatures used in alternate conversion and reactivation stepspracticed in the process.

An East Texas gas oil of 30.7 A. P. I. gravity was heated to atemperature of approximately 940 F. and contacted with the abovedescribed catalyst disposed in l4-foot beds in a plurality of catalysttubes. The pressure at the inlet of the tubes was approximately 40pounds per square inch. The conversion products were fractionated and21.9% of 400 F. end-point gasolinawas obtained having a bromine numberof approximately 90. An intermediate boiling stock corresponding to69.2% of the gas oil charged was separated for processing in `thesecondary step, and 5.7% by volume o f the oil charged of residue wasWithdrawn from the process. Carbonaceous material to the extent of 0.5%by weight of the charging stock was deposited upon the catalyst andremoved by periodic regeneration treatment with oxygen-containing gas.The gasoline produced had a 60.7 A. P. I. gravity, a 10.7 Reid vaporpressure and an octane number of 79.7 by the C. F. R. motor method. Theintermediate boiling product from the primary step had an A. P. I.gravity of 31.7 and was charged to the secondary step and processed at atemperature of approximately 800 F. and an hourly liqui'd space velocityo'f approximately one, using ap-- proximately 50 pounds per square inchpressure. As a result of this secondary treatment, approximately 20% byvolume of the oil charged was obtained as a 300 F. end-point gasolinehaving a brornine number of approximately 29 and an octane number of 78which, upon the addition ci 6 cc. of tetraethyl lead per gallon wasraised to a 93 octane number. The hydrocarbons boiling above the 300 F.end point motor fuel product was directed back4 to the primary stage forfurther treatment in admixture with fresh oil.

Example II In this example a similar catalyst and similar apparatus wasused as in Example I. A Mid- Continent gas oil having a 37.2 A. P. I.gravity was used and was heated to a temperature of approximately 940 F.at a pressure of 45 pounds per square inch. 36% by volume of oil chargedof 400 F. end-point gasoline was obtained having a broznine number of 97and an octane number of 80.5. 45% by volume of the charging stock of ahigher boiling intermediate fraction was separated from the conversionproducts of the primary step and subjected to treatment in the secondstep of the process at a temperature of approximately 820 F. and apressure of approximately 100 pounds per square inch to produce 28% byvolume of the oil charged of 300 F.

amasar Y S end-point gasoline having a bromine number of 21 and anoctane number of '79.` Upon the addi-l tion of 6 cc. of tetraethyl leadper gallon of gason line the octane number was raised to 94.

I claim as my invention:

1'. A process for producing automotive and vaporous conversion productsandcondensing the conversion products heavier than gasoline, subjectingheavier conversion products thus sepn arated to a non-hydrogenatingcatalytic cracking treatment at lower-temperature than employed in thefirst-mentioned cracking step to producei gasoline of lower olefincontent than said olelnic gasoline from said products, and recoveringthe last-named gasolinev thus formed.

,2. A process for producing automotive and aviation fuels whichcomprises contacting hydrocarbon oil with a cracking catalyst at acracking temperature adequate' to produce olenicgasoline, separating thelatter from the resultant vaporous conversion products and condensingthe conversion products heavier than gasoline, subjecting heavierconversion products thus separated to a non-hydrogenating catalyticcracking treatment at lower temperature than employed in thefirst-mentioned cracking step .to produce gasoline of lower olefincontent than said oleiinic gasoline from said products, separating thelast-namedy gasoline from higher boiling hydrocarbons and supplying atleast a portion of the latter to the first-mentioned cracking step.

3. The process of claim l further characterized in that the crackingcatalyst in both conversion steps comprises a calcined composite ofsilica, alumina and zirconia.

4. rllie process of claim 1 further characterized in thatthe crackingcatalyst in both conversion steps comprises a calcined composite ofsilica and alumina.

5. The process of claim 1 further characterized in that the crackingcatalyst in both conversion steps comprises a calcined composite ofsilica and zirconia.

6. A process as set forth in claim 1 wherein the temperature employedvin the first-mentioned conversion step is within the range of S50-200F., and the pressure employed is within the range of atmospheric to 100pounds per square inch.

7. A process as set forth in claim 1 where the temperature employed inthe second-mentioned conversion step is within the approximate range of50o-850 F., and the pressure employed is within the range of atmosphericto about 1000 pounds per square inch.

8. A process for concurrently producing automotive and aviation fuelsfrom a hydrocarbon oil which comprises subjecting said hydrocarbon oilin admixture with a high boiling fraction from a' secondary stephereinafter set forth to contact with a calcined mixture of precipitatedhydrated silica and precipitated hydrated alumina, said mixture beingsubstantially free from alkali metal compounds, at a temperature Withinthe approximate range of 850'-1200 F., and a pressure within the rangeof atmospheric to 100 pounds per square inch, fractionating theresultant vaporous conversion products to separate a gaseous fraction, amotor fuel of relatively high olefin content and heavier hydrocarbonsboiling above said motor fuel, removing the gaseous fraction and motorfuel from the process, and subjecting said heavier hydrocarbons boilingabove said motor fuel from said primary cracking step to anon-hydrogenating catalytic cracking treatment in the presence-of acalcined mixture of precipitated hydrated silica and precipitatedhydrated alumina, saidv mixture being substantially free from alkalimetal compounds, at a temperature within the approximate range of500850'F., and a' pressure Within the range of atmospheric to about 1000pounds per square inch, separating the conversion products yinto anormally gaseous fraction, an aviation base fuel of relatively lowolefin content and a fraction containing hydrocarbons boiling above theaviation base fuel, and returning said high boiling fraction from thesecondary step` to further treatment inv admixture with the ,chargingstock in the primary cracking step. f

9. A process for concurrently producing automotive and aviation fuelsfrom a hydrocarbon oil which Acomprises subjectingsaid hydrocarbon oilin admixture with a high boiling fraction from a secondary stephereinafter set forth to contact with a calcined mixture of precipitatedhydrated oxides of silicon, aluminum and zirconium, said mixture beingsubstantially free from alkali metal compounds, at a temperature withinthe approximate range of 850-1200 F., and a pressure within the range ofatmospheric to 100 pounds per square inch, fractionating the resultantvaporous conversion products to separate a gaseous fraction, a motorfuel of relatively high olefin content and heavier hydrocarbons boilingabove said motor fuel, removing the gaseous fraction and motor fuel fromthe process and subjecting said heavier hydrocarbons boiling above saidmotor fuel from said primaryV cracking step to a. non-hydrogenatingcatalytic cracking treatment in the presence of a calcined mixture ofprecipitated hydrated oxides of silicon, aluminum and zirconium, saidmixture being substantially free from alkali metal compounds, at atemperature within the approximate range of 50G-850 F., and a pressureWithin the range of atmospheric to about 1000 pounds per square inch,separatingy the conversion products into a normally gaseous fraction, anaviation base fuel of relatively low olefin content and a fractioncontaining hydrocarbons boiling above the aviation basev fuel andreturning said-high boiling fraction from the secondary step to furthertreatmenty in admixture with the charging stock in the primary crackingstep.

10. A process forconcurrently producing automotive and aviation basefuels from a hydrocarbon oil which comprises subjecting said hydrocarbonoil in admixture with oil from a secondaryA step hereinafter set forthto contact with a cracking catalyst in a primary stepv under catalyticcracking conditions of temperature and pressure adapted to produceconversion products containing substantial proportions of motor fuelcontaining relatively high proportions ,of olenic hydrocarbons,separating said conversion products to produce a gaseous fraction, saidrmotor fuel of relatively high olefin content, intermediate higherboiling hydrocarbons and a high boiling residue for removal from theprocessl and v subjecting said intermediate higher boiling hydrocarbonsfrom the primary cracking step to a non-hydrogenatlng catalyticcracking' treatl ment in the presence of a cracking catalyst in avconversion products containing substantial proportions of aviation basefuel of relatively low olefin content, s eparating said conversionproducts to produce a gaseous fraction, said aviation base uelpofrelatively low olefin content, and a fraction containing hydrocarbonsboiling above the aviation base fuel and returning said higher boilingfraction from the secondary step to further treatment in admixture withcharging stock in the primary cracking step.

11. A process for producing automotive and aviation fuels whichcomprises catalytically cracking hydrocarbon oil at a temperature in theapproximate range of 850l200 F. and a liquid space velocity of 0.5 to50, thereby forming olenc gasoline, separating the latter from theresultant vaporous conversion products and condensing the conversionproducts heavier than gasoline, subjecting heavier conversion productsthus separated to a non-hydrogenating catalytic cracking treatment at atemperature in the approximate range of 50o-850 F. and a liquid spacevelocity of about 0.5 to 5 to' produce gasoline of lower olen contentthan said olefinic gasoline, and recovering the latter.

12. A process for producing automotive and aviation fuels which,comprises catalyticaily cracking hydrocarbon oil at a temperature in theapproximate range of 850-1200 F. and a liquid space velocity of 0.5 to50, thereby forming oleiinic gasoline, separating the latter from theresultant vaporous conversion products and condensing the conversionproducts heavier than gasoline, subjecting heavier conversion productsthus separated to a non-hydrogenating catalytic cracking treatment at atemperature in the approximate range of SOO-850 F. and a liquid spacevelocity of about 0.5 to 5 to produce gasoline of lower olen contentthan said olefinic gasoline, separating the last-named gasoline fromhigher boiling hydrocarbons and supplying at least a 20 portion of thelatter to the first-mentioned cracking step.

CHARLES L. THOMAS.

